1. Field of the Invention
The present invention relates to a photographic lens system, and more particularly to a photographic lens system having an aperture diaphragm behind all of the lens elements.
2. Description of the Prior Art
Recently, the compactness of the lens system has become a requirement in lens shutter cameras. However, it is difficult to make the lens system more compact, since the lens system is also required to achieve a large angle of view reaching about 60.degree.. Two types of such lens system are proposed, one of which has an aperture diaphragm between the successive two lens elements, and another of which has an aperture diaphragm behind all of the lens elements. The former type has a disadvantage in that it is difficult to correct all of the aberrations well in various object distances if one or plurality of the lens elements located at the object side of the aperture diaphragm are shifted in the focusing operation, since the change of the aberrations is excessively large in the focusing operation.
On the other hand, the latter type also has a disadvantage in that it is difficult to make the lens system compact. The disadvantage is caused by the difficultyof correcting the distortion well while maintaining good correction of the field curvature. Namely, in order to make the lens system more compact it is necessary to apply a telephoto type power arrangement in which a positive refractive power is located at the object side and a negative refractive power is located at the image side thereof. Thus, the positive refractive power located at the object side should be increased for making the lens system more compact, while the resulting positive distortion and the deterioration of the field curvature is corrected by the decrease of Petzval sum. Here, the deterioration of the coma aberration generally results even if both the distortion and the field curvature are well corrected.